This invention relates to an improved driving device whereby the elevator driven by an A.C. motor may be driven in an emergency as during a power supply interruption.
Usually, in case of a power supply interruption at the power source for an elevator, the elevator is continued to be driven by a switchover from said power source to an emergency power source. FIG. 1 shows a drive device which is used at the time of power supply interruption, wherein the motor for driving the elevator car is an induction motor and is driven by an A.C. power of a variable frequency.
In the drawing, the numeral 1 designates a three-phase power source, and the numeral 2 a converter for converting A.C. power having a constant frequency into A.C. power having a variable frequency, as will be described below. The numeral 3 designates an emergency power source such as a battery. The numeral 4 designates an emergency inverter for converting the D.C. power from the emergency power source into a three-phase A.C. power of the constant frequency. The numeral 5 designates a normal operation contact connected to the converter 2 and turned "on" and "off" during normal operation and at the time of a power supply interruption of the three-phase A.C. source 1, respectively. The numeral 6 designates a supply interruption contact connected to the emergency converter 4 and turned "on" and "off" at the time of supply interruption and at the time of normal operation, respectively. The numeral 7 designates a three-phase induction motor connected to both the contacts 5, 6. The numeral 8 designates a drive sheave of a winch driven by the motor 7. The numeral 9 designates a main cable wound about sheave 8. The numerals 10, 11 designate a car and a balance weight coupled to both ends of the main cable 9, respectively.
During normal operation, the contact 5 is closed, so that the A.C. power of variable frequency is supplied to the motor 7 for controlling the speed of the car 10. During supply interruption, the contact 5 is opened and the contact 6 closed, so that A.C. power is supplied to the motor 7 from the emergency inverter 4 for driving the car 10.
This conventional device has, however, a drawback in that the drive means employed during a supply interruption tend to be costly because of the provision of the emergency inverter 4.